In a cooperative effort between the KlimaCamus of the University of Hamburg, the German Oceanographic Data Centre (DOD, Hamburg), the PANGEA Publishing Network for Geoscientific & Environmental Data and the Alfred Wegener Institut für Polarforschung (AWI), we aim to combine all available global historic hydrographic data and quality control them in the context and in support of ocean state estimation. However, there is a general need in the oceanographic community for a historic hydrographic data set providing quality-controlled temperature and salinity profiles as long backwards in time as possible. Such a data set will be important for many different applications in the oceanographic community since it will provide a description of the two most important characteristics of sea water. Applications will include water mass analysis, ocean modeling but especially also ocean syntheses estimating the time-varying ocean circulation by combining all available ocean data with ocean models. Our first goal is to create an up to date hydrographic profile data set, which includes temperature and salinity measurements, obtained by means of the old Nansen hydrographic casts and by the modern Conductivity/Temperature/Depth (CTD) instruments. These two kinds of data are by far the most accurate compared to other instrument types. Efforts are spend to include many German data sets not included in the historic data archives before, as well as other data obtained in the past over the global ocean. We extend the quality control procedure of the World Ocean Database 2005 in several ways. The T and S quality checks will be conducted in the T/S-space and inter-cruise offsets will be calculated wherever possible. As shown by Johnson et al, 2001 and by Gouretski and Jancke, 2001 systematic offsets between the cruises exist even for the data of the highest available quality (e.g. WOCE data set). Such inter-cruise offsets will be determined and documented on a cruise by cruise basis. The metadata, most important for the quality assessment of the temperature and salinity data, will be also provided (if available) along with profile data on a cruise by cruise basis. Data processing methods developed during the initial stage of the project will be used for the analysis of other types of hydrographic subsurface data, such as those from mechanical and expendable bathythermographs and profiling floats. The hydrographic cast data will be used as a reference for the quality assessment of data from other instruments.Data will be world-wide available on the KlimaCampus data server www.klimacampus.de